Tourniquet is usually performed in the sites such as the drawing blood by, for example, winding an elastic band around the arm of human body. However, nurses and so on conventionally depend on their own sense and decide constricting strength of the rubber band by themselves. Therefore, constricting strength is either too weak or too strong, and it is difficult to constrict the arm with appropriate tourniquet pressures. Therefore, the development of the simple auto electronic tourniquet which can automatically constrict the arm with appropriate tourniquet pressures has been expected.
On the other hand, as a tourniquet which could automatically perform tourniquet to some extent, the one has been known which comprises a manchette mountable to the arm of the human body, a pressure-applying means pressurizing the manchette, and a blood pressure measuring means for measuring the systolic blood pressure (maximum blood pressure) and the diastolic blood pressure (minimum blood pressure) of the person who mounted the manchette by either pressurizing or depressurizing the manchette with the pressure-applying means. The tourniquet is configured to perform tourniquet by measuring the diastolic blood pressure and the systolic blood pressure with the blood pressure measuring means and by setting pressures of the manchette between the diastolic blood pressure and the systolic blood pressure (e.g., reference cited 1).
In the tourniquet configured in such a way, the manchette is mounted to the arm first, and then the manchette is pressurized to pressures higher than the expected systolic blood pressure and is gradually depressurized. In the depressurizing process, the diastolic blood pressure and the systolic blood pressure are measured based on changes of the biological signal.
That is, in the depressurizing process, since developments of the Korotkov's sound, for example, as changes of the biological signal are detected, the systolic blood pressure is measured with pressures of the manchette at the time of detection. By continuing depressurizing, since disappearances of the Korotkov's sound are detected next, the diastolic blood pressure is measured with pressures of the manchette at the time of detection of disappearances. After that, the manchette is pressurized again, and pressures of the manchette are set in predetermined pressures between the diastolic blood pressure and the systolic blood pressure, by which tourniquet is performed.
By performing tourniquet in the above-described way, while the arterial blood flow is maintained, the venous blood flow is suspended and the vein is made dilated surely, by which venipuncture can be performed easily.
However, when the systolic blood pressure is detected with using the above-mentioned tourniquet, as the arm must be pressed in a pressure well beyond the systolic blood pressure, a problem is that pain is felt in the arm on the occasion. Besides, both of the systolic blood pressure and the diastolic blood pressure are measured, and then pressures of the manchette are set in a predetermined pressure between the systolic blood pressure and the diastolic blood pressure. Therefore, another problem is that much time is needed in the preparatory stage before venipuncture.